The long-term goals are to understand the functional organization of brainstem "initiation" or "command" systems which activate the spinal motor networks for locomotion in vertebrates. An understanding of these systems will require information regarding the locations of relevant neurons, their cellular and synaptic properties, and their activity patterns during the initiation of locomotion. The proposed project involves a physiological and anatomical analysis of the brainstem command systems for swimming in the central nervous system of a primitive vertebrate, the lamprey. I have developed an in vitro brainstem/spinal cord preparation, which generates functional motor activity and which can be used to provide detailed cellular information. The CNS is completely exposed in this preparation, so it is relatively easy to manipulate part or all of the extracellular recordings. Sensory stimulation of the head or electrical microstimulation applied to parasagittal "brainstem locomotor regions" elicits swimming motor patterns recorded in spinal ventral roots. I will use this model system to study the integrative and cellular properties of vertebrate command systems. The goals are to progress in several steps towards gathering detailed cellular information about the command neurons for swimming in the lamprey brainstem. First, I will test if the "brainstem locomotor regions" are necessary for initiating swimming by lesioning these areas and then determining if the initiation of locomotion is blocked. Second, the locations of descending neurons in the brainstem command systems will be determined by both an anatomical method using HRP and a chemical stimulation method using microejection of excitatory amino acids. Third, chemical stimulation will be used to activate and thereby locate cells presynaptic to the descending neurons in the command system. Finally, having located putative command neurons in the systems, I will then perform intracellular recording and staining of these cells to characterize 1) their cellular properties, 2) their activity during initiation of swimming, and 3) their projections to the spinal motor networks. These studies will provide new and detailed cellular information about the function of brainstem command systems for vertebrate locomotion.